期刊
BIOSCIENCE BIOTECHNOLOGY AND BIOCHEMISTRY
卷 75, 期 8, 页码 1557-1563出版社
TAYLOR & FRANCIS LTD
DOI: 10.1271/bbb.110256
关键词
dextran glucosidase; thermostability; two-step irreversible deactivation; calcium-binding site; glycoside hydrolase family 13
类别
资金
- Grants-in-Aid for Scientific Research [22880043, 22658032, 21405020, 22580099, 22780082] Funding Source: KAKEN
Dextran glucosidase from Streptococcus mutans (SmDG), which belongs to glycoside hydrolase family 13 (GH13), hydrolyzes the non-reducing terminal glucosidic linkage of isomaltooligosaccharides and dextran. Thermal deactivation of SmDG did not follow the single exponential decay but rather the two-step irreversible deactivation model, which involves an active intermediate having 39% specific activity. The presence of a low concentration of CaCl2 increased the thermostability of SmDG, mainly due to a marked reduction in the rate constant of deactivation of the intermediate. The addition of MgCl2 also enhanced thermostability, while KCl and NaCl were not effective. Therefore, divalent cations, particularly Ca2+, were considered to stabilize SmDG. On the other hand, CaCl2 had no significant effect on catalytic reaction. The enhanced stability by Ca2+ was probably related to calcium binding in the beta -> alpha loop 1 of the (beta/alpha)(8) barrel of SmDG. Because similar structures and sequences are widespread in GH13, these GH13 enzymes might have been stabilized by calcium ions.
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